Thin-layer chromatography arose from paper chromatography, which was developed in 1944 in protein research by Consden, Gordon and Martin. Both methods work with a stationary phase upon which a dissolved speciman of the material to be analyzed is placed, and with a mobile phase, a solvent in which the carrier is dipped with one end. The solvent travels by means of capillary action in the stationary phase and carries along the individual substance of the specimen at differing speeds, depending on the absorption properties. The separation of the substances is the result of the reciprocal action between the specimen of the sorption layer (stationary phase) and the developing solvent (mobile phase), as well as the gaseous phase.
In thin-layer chromatography, abbreviated as TLC, a glass plate or a sheet of plastic or aluminum is usually used as the carrier of the sorption layer.
The feed of the solvent onto the sorption layer of a carrier in a closed TLC chamber can take place in various ways. Known methods are:
(1) by dipping the edge of a TLC carrier into the flow agent;
(2) by solvent bridges made of filter paper, porous material, etc., which are in contact both with the solvent agent and also with the sorption layer of the TLC carrier;
(3) by the supplying of flow agents over a round or long capillary tube from a solvent vat directly onto the sorption layer; or
(4) by a reproducible force-feed with a dosing system, e.g., pump, syringe, etc.
As is known, the travel speed of the solvent in the absorption layer decreases with the square of the distance traveled, which necessitates considerable development times in long distances to be traveled. However, the development time can be shortened by forced feeding or a reproducible overfeeding of the flow agent. This can simultaneously improve the dissolution of the separate spots and decrease the diffusion. Unfortunately, however, this method requires an expensive apparatus and was previously known and possible only for circular TLC.
Other disadvantages of previous TLC methods are the small number of ways of carrying out the method and the relatively small dosing surface. The known types of methods are:
(1) the linear TLC, i.e., the solvent travels from one side to the other side of the plate or sheet;
(2) the circular TLC, i.e., the solvent travels from the center outward in all directions; and
(3) the anticircular TLC, i.e., the solvent travels from the periphery to the center of the sorption layer.